This invention relates generally to dental syringes, and more particularly to a fitting for releasably connecting a syringe tip to a hand piece for delivering a fluid to a mouth of a patient.
Dental syringes are hand-held devices for discharging fluids, such as pressurized air and water, into a patient's mouth. Syringes typically have a hand piece for gripping by a hand of a dentist or dental assistant and a fitting adapted for receiving a detachable tube or tip. Such syringes are described in U.S. patent application Ser. No. 08/787,243, filed Jan. 24, 1997, now U.S. Pat. No. 5,927,975 which is hereby incorporated by reference. Fluids are conveyed through the hand piece and the fitting to the tip which delivers the fluids to the patient's mouth. The tip must be securely held by the fitting to prevent it from being ejected into the patient's mouth, and it must be clean to avoid spreading disease. To ensure the tips are clean, dentists typically change tips after each patient.
Ideally, a dentist should be able to quickly and securely lock a new tip in place. Unfortunately, many syringes of the prior art do not provide this ability. For instance, some fittings hold the tip in place with ball bearings which engage a circumferential groove extending around the tip. To use these fittings, the dentist must first depress a collar to permit the ball bearings to move radially outwardly so the tip can be inserted, and thereafter allow the collar to return to a locking position wherein the ball bearings are moved inwardly to engage the groove and lock the tip in position. These steps require the dentist to use both hands and can be awkward. Further, if the collar has not properly returned to its locking position, the tip remains loose and may be ejected from the syringe, posing a potential safety hazard.
Other fittings hold the tip with elastomeric O-rings which engage the circumferential groove around the tip. Although these fittings grip a new tip automatically when it is inserted, they rely solely on friction and elasticity from the O-rings to oppose removal of the tip. Because the magnitude of the frictional force is relatively limited, the tip is subject to ejection from the fitting when exposed to a strong force. Further, O-rings degrade over time which can diminish their elasticity and ability to generate frictional force, making the fitting unreliable.